The invention relates to a method of providing electronic zoom and electronic pan and tilt capabilities in digital imaging applications, and more particularly to an electronic camera wherein the electronic zoom and electronic pan and tilt functions are seamlessly interfaced.
Electronic cameras which can be moved mechanically to rotate about a vertical axis (pan), about a horizontal axis (tilt) and to change the magnification of the displayed imaged by changing the focal length of the camera lens (zoom) are known in the art. Since mechanical control of pan, tilt and zoom (xe2x80x9cMPTZxe2x80x9d) is rather expensive, electronic cameras have been developed which exclusively utilize solid state components to pan, tilt, and zoom. An electronic pan, tilt, zoom (xe2x80x9cEPTZxe2x80x9d) camera is small, fast, inexpensive, quiet, reliable, durable, easy to manufacture and easy to upgrade. If the requirements for resolution and image quality are modest, such as in most video conferencing applications, such cameras can have an imaging lens with a fixed focus and a stationary support, i.e., no mechanical movement of the camera body or of components within the camera.
In MPTZ cameras, panning, tilting and zooming are performed independently of each other. For example, if the camera is panned to the right as far as it can go, the lens is still free to zoom out and in to any position, from full wide angle to full telephoto, which can represent a factor of 25 to 30 in image magnification. On the other hand, in a stationary EPTZ camera having a fixed focus setting, panning, tilting and zooming operations are performed by selecting electronically a subset of pixels from all the pixels of the camera""s image sensor. The image is zoomed in by selecting the subset of pixels from, for example, one fourth of the image area, corresponding to a zoom ratio of 2, and the image is panned/tilted by locating the subset of pixels in different areas on the image sensor. Tilting/panning are therefore not completely independent of each other, since an image can be panned/tilted only so far, until an edge of the subset of pixels of the zoomed image reached the edge of the image sensors. For example, if the camera is zoomed out to the widest possible view (full wide angle), then all pixels of the camera""s image sensor contribute to the image to be displayed so that electronic panning or tilting is not possible since otherwise the subset of pixels would fall outside the pixel area of the image sensor. In a different situation, if the camera is zoomed in so that the subset of pixels is smaller than the pixel area of the image sensor and the image is subsequently electronically panned and/or tilted by forming the subset of pixels from pixels which are located closer to a lateral edge of the image sensor, the image can only be panned and/or tilted until an edge of the subset of pixels overlaps with the lateral edge of the image sensor. Alternately, if an image which is panned or tilted, is subsequently zoomed out, the image can only be zoomed out until an edge of the subset of pixels hits the lateral edge of the image sensor.
Conventional MPTZ camera adjustments are usually performed in a particular order. For example, starting at full wide view, a user would typically frame an object on, for example, the right side of the field of view by first panning the camera mechanically until the object is centered. The user would then zoom in until the object is framed with the desired magnification (zoom ratio). However, since an EPTZ camera in full wide view cannot pan or tilt, as described above, the user would first have to zoom in, with the possibility that the object moves out of the frame; the user would subsequently pan to the right, bringing the object back into the frame, then make final zoom adjustments, possibly switching back and forth between panning and zooming to bring the object close to a position which is centered in the displayed image. This process can be time consuming and frustrating.
It is therefore an object of the present invention to overcome these disadvantages by integrating in an EPTZ camera the zoom function with the pan and tilt function.
The object of the invention is solved by an electronic zoom system which includes an electronic camera with an image sensor with pixels, a controller communicating with an address generator to select a subset of pixels from the pixels of the image sensor, with the subset of pixels defining a zoom area. The zoom area can be located at any position within the image sensor area, with the defining pan and tilt of the zoom area. The zoom ratio/pan/tilt of the zoom area is automatically adjusted so as to maintain the location of the zoom area entirely within the image sensor area.
In an advantageous embodiment, the controller supplies data to the address generator to adjust the zoom ratio as a function of the respective pan and tilt position so that the zoom area is located entirely within the imager area. For example, if the image pans and/or tilts so far that a lateral edge of the zoom area abuts the lateral edge of the image sensor, then the image can continue to pan and/or tilt while at the same time, the image is zoomed in, i.e., the size of the subset of pixels is decreased, so that the lateral edge of the zoom area is prevented from crossing over the lateral edge of the image sensor. The zoom/pan/tilt operation is here completely linked and integrated so that the user or an automatic system, as mentioned above, will only have to select and electronically xe2x80x9caimxe2x80x9d at the object to be imaged.
In another advantageous embodiment, the scaler automatically adjusts the pan and/or tilt position if a panned and/or tilted image is subsequently zoomed out (i.e., demagnified), so that the lateral edge of the zoom area is prevented from crossing over the lateral edge of the image sensor.
In yet another advantageous embodiment, the electronic camera is incorporated in a set-top box for video conferencing and has preferably an imaging lens with a fixed focal length.
In still another advantageous embodiment, the zoom system is responsive to characteristic image attributes, such as movement of an object, or environmental settings, such as sound or optical signals, e.g., a light beam emitted by a pointer.
In another advantageous embodiment, the electronic zoom/pan/tilt functions are incorporated in a scanner adapted to scan, for example, photographic images. A user can then use, for example, the control commands available on the user interface to zoom and pan/tilt the displayed image and the control electronics automatically adjusts, if necessary, at least one of the zoom ratio and the pan/tilt positions in response to changes in the other, so that no portion of the zoom area is located outside the image area.
The invention advantageously also provides a method for electronically zooming, panning and tilting an image. A zoom area is selected from an image area together with a pan and/or tilt position of the zoom area. When the displayed image is to be changed, a combination of the zoom area and the pan and/or tilt positions are adjusted so that no portion of the zoom area is located outside the pixel area of the imager.